1. Field of the Invention
The present invention relates to an improved router cutting bit, and in particular to a router cutting bit for cutting metal parts such as aluminum parts.
With the improved router cutting bit according to the invention the cut surface is provided with a smooth resultant finish absent rough edges.
2. Prior Art
In the manufacture of aluminum parts, for example for aircraft, the resultant finish on the cut surface of the aluminum part must meet standards specified by all aircraft manufactures (125 rms finish). If the cutting bit used in the cutting operation does not produce such a finish it becomes necessary to subject the part to a secondary finishing operation which can involve both polishing and deburring. The time and expense associated with the secondary finishing operation can be quite significant and therefore undesirable.
It is found that the cutting of different steels with a router cutting bit does not require as much of a secondary finishing operation as does aluminum, and in particular soft aluminum ("0" condition). Perhaps the inherent "softness" of aluminum relative to steel accounts for the difference. For either material, a typically constructed router cutting bit includes both primary and secondary lands on its outer surface adjacent to the cutting tip. An example of such a bit is disclosed in U.S. Pat. No. 4,560,308.
At the outset, it was presumed that the commercially available router cutting bits used for steel as well as other "hard" metals and having both primary and secondary lands could be used successfully to cut aluminum and in particular the noted soft aluminum to the proper finish in a single operation. However, extensive experience has shown that this was not the case. Over a period of two years numerous router cutting bits having different angles and helixes were used without ever achieving the 125 rms finish. Many of the router cutting bits were offered by tool manufacturers after being appraised of the problem presented, still with negative results.
The following table summarizes several of the bits that were tested.
__________________________________________________________________________ Primary Secondary Radial Outside Diameter Outside Diameter Rack Cutter Type Clearance Clearance Angle Remarks __________________________________________________________________________ Onsrud -40 -106 .250 5.degree. 12.degree. 10.degree. Surface texture too rough downcut *H.S.S. 2 flute Bay state .250 2.degree. 15.degree. 15.degree. Secondary angle ground with downcut carbide 2 flute a step finish poor Onsrud 43-002 and 12.degree. 10.degree. 15.degree. Severe abrasion and chatter rbl 202220 and surface rough ER -69 - ES .250 H.S.S. downcuts (3) cutters, 1 flute National Paraflute 0.degree. 12.degree. 18.degree. Modified drill rout H.S.S. router bit 123.F severe abrasion Basset .375 shank turned 8.degree. 15.degree. 18.degree. Upcut cutter pulls chips back down to .250 2 flute into cutter path instead of upcut, carbide away from __________________________________________________________________________ *High Speed Steel